Pulse echo range azimuth and elevation presentation



March 3, 1953 L. J. HAWORTH 2,630,563

- PULSE ECHO RANGE AZIMUTH AND ELEVATION PRESENTATION Filed May 25, 19442 SHEETS-SHEET 1 TRIGGER PUL 55' i I l 20 l AZ/MUTH 33 E INVENTOR.LELAND JHA WORTH EL Em r/0/v AZ/MU TH A/hr/rer March 3, 1953 J. HAWORTH2,630,563

PULSE EbHO RANGE AZIMUTH AND ELEVATION PRESENTATION Filed May 25, 1944 2SllEETS-SHEET 2 FIG-4 INVENTOR.

LELAND J HAWORTH Patented Mar. 3, 1953 PULSE ECHO RANGE AZIMUTH ANDELEVATION PRESENTATION Leland J. Haworth, Belmont, Mass., assignor, bymesne assignments, to the United States of America as represented by theSecretary of War Application May 25, 1944, Serial No. 537,319

3 Claims.

This invention relates to a communication system and is an improvementupon the system disclosed and claimed in the co-pending jointapplication of Leland J. Haworth and Edward M. Purcell, Serial No.531,826, filed 19th April 1944, now Patent No. 2,606,318 issued Aug. 5,1952. The system described in the above referred application is a radarsystem for searching and locating targets. The search system disclosedtherein comprises the usual transmitter, receiver and antenna systemwith target indications being presented on a cathode ray tube screen.The antenna system is a highly directive system having a beamcharacteristic. In order to provide adequate scanning, means areprovided for rotating the antenna, which in this instance includes aparaboloid reflector, about a longitudinal axis and also oscillatingsaid reflector about a transverse axis. The combination of these twomotions provides a spiral scan with the beam tracing increasing anddecreasing spirals over the field to be scanned.

One of the important phases of the invention disclosed and claimed insaid application resides in the manner of target presentation. Asdescribed therein, the target is presented in the form of a fluorescenttrace consisting generally of straight lines inclined at some angle toone of the screen axes, in this particular instance,

the horizontal axis. The beginning of the trace I is determined by therange and azimuth of the target, while the angle of the line to thehorizontal gives the elevation with respect to the antenna system. Ithas been found that in such a system the generation of continuous lineartraces increases to an objectionable degree the ratio of signal tonoise. Furthermore, the presentation of targets in this manner makes fora relatively complicated electrical system.

The invention hereinafter disclosed and claimed improves upon theinvention disclosed and claimed in the above identified application bychanging the target presentation. The invention herein provides aso-called two-dot system of target presentation. The two dots may beequivalent to the starting point and an additional point on the lineartrace of the above disclosed system. By virtue of such a presentation, asubstantial improvement in the signal to noise ratio is provided; and,in addition, the system lends itself to simplification.

In general, the presentation of a target is made by a point trace on thescreen in a manner well known to the art. The location of the point maybe determined by the range and azimuth of the target. The second pointis obtained by merely shifting the entire frame of the scanning area onthe tube screen a predetermined amount. Thus after the frame is shifted,the target is presented as a dot again but now displaced from 2 thefirst dot. The displacement. of the tube screen field of scan isdetermined by the angular coordinates of the target. It is understoodthat azimuth and elevation may be interchanged so that the angle of theline joining the two dots may indicate azimuth instead of elevation. Itis understood that the shifting of the scanning area frame does notrequire the scanning of one complete frame and then the scanning of theother frame. Actually, the two frames are interleaved in a time sense,with a line or range element of one frame being generated and thenfollowed by the corresponding line or range element of the other frame.

In general, the invention contemplates the alternate switching by meansof transmitter pulses of what might be termed normal and displacedscreen scanning fields.

For a more complete description of the invention, reference will now bemade to the drawing wherein Fig. 1 is a diagrammatic representation ofone scanning procedure illustrating several different stages in themovement of the beam, together with corresponding cycles of analternating current wave used for controlling the beam, it beingunderstood that the beam is actually suppressed except when targetpresentation data is made;

Fig. 2 is a front view of a cathode ray tube screen showing targetpresentation of the system;

Fig. 3 is a circuit diagram, partly in blocks, of the two-phasegenerating system associated with the antenna to provide voltages whoseamplitude and phase correspond to the location of the antenna beam inspace; and

Fig. 4 is a circuit diagram of the indicating portion of the system.

In Fig. 1 are shown five different representations of the face of acathode ray tube l, which may be the indicating device of the system,illustrating how the electron beam is moved to produce the relativeazimuth and range of the object or objects represented on the face ofthe tube when spiral scan is used. As the beam of electromagneticradiation traces the spiral scan in space, the electron beam in thecathode ray tube is caused to move from side to side, the displacementfrom the center of the tube at all times corresponding to the horizontaldisplacement of the electromagnetic beam from the axis about which thespiral is formed. At the same time the electron beam in the cathode raytube is caused to sweep vertically from a line across the lower edge ofthe face of the tube to a line across the upper edge of the face eachtime a pulse of electromagnetic radiation is transmitted, and the rateof movement of the electron beam during each vertical sweep may belinear. The pulse rate of the electromagnetic radiation is very fore, asthe electron beam in the cathode ray tube:

moves from side to side in synchronism with the side to side movement oftheelectromagnetic beam, the sweeps of the electron beam in the cathoderay tube will come very close together and will be substantialyvertical. A single field of scan on the tube screen will be assumed.

At the left in Fig. 1 the face of the cathode ray indicator tube I isreoresented'at a time when the spiral scan of the electromagnetic beamstarts from the center'of the scanning spiral. The first half-cycle ofthe spiral is indicatedby small, curved line (1 immediately above tubeI. During the time that the electromagnetic beam is passingthrough thishalf-cycle at the start of the spiral scan, the electron beam in theoathode ray tube is producing perhaps as many as fifty vertical sweeps,as indicated by solid vertical lines b. These vertical sweeps willproduce no visible indication on the face of the tube, as will be laterexplained.

Circle 2 in Fig. 1 represents the face of indicator tube I after thespiral scan has passed through a cycle and a quarter shown atc. Therepeated vertical sweeps have moved toward the left across the centerline of the tube and have moved back again toward the right as thespiral completes the next quarter cycle, the lines passing farther tothe right as the electromagnetic beam reaches the extreme right side ofthe spiral turn. This is shown at d.

Circle 3 represents the face of indicator tube I at the time. when theelectromagnetic beam has reached the maximum outerturn of its spiral,this. turn being indicated at e in the spiral immediately above circle3. The repeated sweeps of the electron beam of the cathode ray tube bythis time have reached the extreme left and right side of the tube,asrepresented by lines so that the entire face of the cathode ray tubehas been covered by the repeated vertical sweepsof the electron beam.Each turn of the spiral requires the same time as every other turn, and,since there are the same number of sweeps for each cycle, it will beseen that; as the radius of the spiral increases, the Vertical sweepswill be farther apart. v Now the radius of the spiral which theelectromagnetic beam is tracing begins to decrease, and vertical lines 9on cathode ray tube I represented by circle 4 will be formed, with theirmaximum side positions nearer and nearer to the center, as the spiraldecreases in radius. Spiral h immediately above circle 4 illustrates thesecond half of the spiral where the radius is receding, the first half,shown above circle 3 having been omitted for clearness. The width of theportion of the tube covered by lines g is shown as corresponding to theinner half-cycle of spiral h.

As the spiral continues to decrease in radius, the vertical linesapproach nearer and nearer to the center until a single line 7' isformed at the center, as indicated in circle 5 which represents cathoderay tube I at'the end of a complete scanning cycle. The lastthree-quarter turn of the spiral is indicated at k. 7

- It will thus be seen that repeated vertical sweeps of the electronbeam in cathode ray tube I are caused by the repeated pulses ofelectromagnetic radiation and that these sweep lines are caused to startfrom the center of the cathode ray tube when the axis of theelectromagnetic beam coincides with the axis of revolution and to movefrom side" to side, reaching ever-increasing distances from the centeras the electromagnetic beam traces its spiral path, and then, after themaximum position has been reached, to continue to move from side to sidebut with ever-decreasing distances from the center of the tube, as

' the spiral trace approaches its center again. This causes the verticalsweeps of the cathode ray tube to have a bellowslike action as theelectromagnetic'beam scans the field in a spiral pattern.

Simultaneously with the spiral scanning of the electromagnetic beam, analternating voltage, preferably in the general form of a sine wave, isproduced in a manner to be later described at a frequency equal to thefrequency of revolution of the electromagnetic beam and having aninstantaneous value which is proportional to the cosine of the angle ofrevolution of the beam. Thus one cycle of the alternating voltagecorresponds to one cycle or turn in the spiral path of theelectromagnetic beam. This alternating voltage is modulated, in a mannerto be later described, by the movement of the electromagnetic beam fromside to side. This alternating voltage is illustrated diagrammaticallyby the sine wave represented above each of the spiral diagrams inFig. 1. Thus curve m represents a halfcycle of the sine wave as itstarts from zero and rises to an amplitude corresponding to thehorizontal displacementof the electromagnetic beam. Wave n shows thatportion of the sine wave corresponding to spiral curve. 0, the amplitudehaving increased. Wave 10 shows the sine wave at its maximum amplitudewhen the electromagnetic beam has moved to its outermost position.Thereupon the amplitude of the sine wave starts to decrease, asindicated in. wave q, corresponding to spiral hfiof decreasing radius,and wave 1. indicates the voltage sine wave reducing to zero again bythe electromagnetic beam crossing the center of its field of scan whereit coincides with the axis of revolution. As the electromagnetic beamcrosses the center, the phase of the. sine wave is reversed, asindicated. by dotted line 8, in a manner and for av purpose to be laterdescribed.

In, Fig. 2 is shown a representation of the face of cathode ray tube Iwith the type of indication produced by spiral scanning of theelectromagnetic beam, as described above. The electron beam of thecathode ray tube continues to sweep vertically as each pulse ofelectromagnetic radiation is transmitted, the beam tracing invisiblelines which have been represented in Fig. l as lines D, d, f, g and 7'.These may be entirely invisible until reflected radiation received bythe apparatus is caused to intensify the beam. When the signal caused bysuch reflected radiation from an object in space is received, theelectron beam is intensified, so that a spot of light 6 is produced onthe face of the tube in a manner well known in the art. This spot isproduced by the beam covering what might be called the normal field ofscan I on the tube screen. When the next target echo has been receivedby the system, the field of scan of the beam on the screen of the tubehas been shifted as shown by the dotted rectangle 8 So that the spot oflight due to the target is correspondingly shifted as shown at 9.

While the shift of the field of scan of the tube may be. in anydirection, it is preferred to move the same in the same direction at alltimes to provide for uniform target presentation. To

this end, the shifted field of scan of the beam on the screen of thetube will be moved to the right, either up or down with reference to theoriginal field of scan, depending upon the elevation angle. Thus if theelevation angle is positive, namely above the observer, then the shiftedfield of scan will be moved to the ri and up. Conversely, if the angleof elevation is negative, or the target is below the observer, then theshifted field of scan will be moved to the right and below the originalfield of scan. In the event that the elevation angle is rero, in whichcase the target is on a level with the observer, then the shifted framewill be moved to the right, and the two target dots will be horizontallyin line. of beam travel for Fig. 1 requires a vertical displacement oflines to accommodate elevation data.

As disclosed in the aforementioned Haworth and Purcell application, theantenna system is a relatively complicated mechanism whereby a dipoleand paraboloid reflector are spun around the paraboloid axis while thedipole and paraboloid are rocked transversely to said axis. Inasmuch asmany modifications of the mechanism for accomplishing spiral scanningare possible, no detailed description of such mechanism will be given;and for a complete disclosure of such mechanism, reference will be madeto the aforementioned joint application.

Referring now to Fig. 3, a paraboloid is shown diagrammatically, itbeing understood that thi paraboloid includes a properly disposed dipolewith reflector so that proper radiation of energy from paraboloid l maybe effected. Paraboloid I0 is spun on its axis I by a suitable motor |2.At the same time, paraboloid I!) is rocked back and forth by a sectorgear I engaged by a gear I6 driven by a rocking motor |1. It isunderstood that motor I1 oscillates paraboloid Ill up and down as shownin dotted positions, the oscillations being effected eit er by repeatedreversal of motor I1 as disclosed in said joint application or by someoscillating mechanism between a continuously running motor andparaboloid In. In any event, it is to be understood that gear IS andsector gear I5 ha e a limited field of travel for oscillating paraboloidII) with respect to axis Spin motor I2 also drives a two-phase generator2'! which is accurately geared to the motor shaft with respect toparaboloid l0. Thus twophase generator 2|! is driven in one-to-one timedrelation. Two-phase generator 20 has windings 2| and 22 in each of whichis generated a sine wave. Since these waves are displaced 90, one may beconsidered as a cosine wave, while the other is a sine wave. By properlytiming the mechanical connection between generator 25 and paraboloid III, it is possible to have the peak of one sine wave coincide with apredetermined spin position of paraboloid I0. Thus, as one example. whenthe paraboloid system is in the position shown in the drawing, namelywith gears I5 and 5 vertical, the instantaneous voltage from winding 2|may be zero, while the voltage from winding 22 will be at maximum. Hencethe output of winding 2| may be considered as a sine wave and the outputof winding 22 as a cosine wave. It is evident that since the rotor ofgenerator 26 has its rotary position corresponding at any instant to therotary position of paraboloid II) that the instantaneous volta esgenerated will correspond to the instantaneou angle of the paraboloidsystem with::reference to some It is evident that the analysis fixedposition where the angle is arbitrarily taken to be zero.

Since the output of generator only gives indications of the rotaryposition of paraboloid II], it is necessary to provide an additionalmeans for giving an instantaneous indication of the eccentricity of theparaboloid, namely the defiection or rocking of the paraboloid from itsnormal symmetrical position as shown in full lines. To this end, gear I6may have controlled thereby a pair of wipers and 26 running overpotentiometer windings 21 and 28. It is understood that potentiometerwindings 21 and 28 are wound in such a fashion that rotary movement ofwipers 25 and 26 will vary the effective resistance of potentiometerwindings 21 and 28 to grounded gear HS. Potentiometer winding 21 hasleads 3!] and 3| connected across the ends thereof and to which areconnected generator windings 2|. Lead 30 goes down to a terminal 32,while between this terminal and lead 3| is a load resistance 33.Similarly, potentiometer winding 28 has leads 34 and 35 across whichgenerator winding 22 is connected. Lead 34 goes to a terminal 36, andbetween this terminal and lead 35 is a load resistance 31.

It is clear that between terminal 32 and ground there will be asinusoidal voltage due to winding 2| with the amplitude thereofmodulated by the movement of wiper 25 on potentiometer winding 21.Similarly, between terminal 36 and ground there will be an amplitudemodulated cosine wave. This two-phase generating system is shown in moredetail and described in the joint application previously referred to.

A receiver and transmitter shown in blocks (Fig. 3) may be connected bya suitable line or transmission system to a dipole cooperating withparaboloid III. In accordance with usual practice, switching meansbetween the receiver and transmitter may be provided for protecting thereceiver against transmitter energy and disconnecting the transmitterduring the time between transmitter pulses when the receiver issensitive to target echoes. From the transmitter a line is provided forconducting a trigger pulse to the indicating system to be described.This pulse may be derived either from the transmitter, as shown, or froma separate timer.

Referring now to Fig. 4, a trigger pulse receiving terminal is provided.Terminal 58 is connected through a blocking condenser 5| to grid 52 of avacuum tube 53. Vacuum tube 53 has its cathode 54 connected to groundthrough a uitable bias resistor 55, while its anode 55 is connectedthrough a pair of load resistors 51 and 58 in series to a junction point59 and thence to a suitabl source of 13+ potential. Cooperating withvacuum tube 53 is a vacuum tube 50 to form a delay multivibrator. Vacuumtube 60 has its cathode 6| connected to cathode 54. Grid 62 of this tubeis connected between two resistances 63 and 64 forming a voltagedividing network between anode 55 and ground. Across resistance 3 is acondenser I55. Vacuum tube 60 has its anode 66 connected back to grid 52through a blocking condenser 61, while the anode itself is connectedthrough two load resistors 68 and 69 in series to a junction point 1!!connected to junction 59 by a wire 1|.

' Grid 52 of tube 53 is also connected to the movable contact 13 of aswitch having three contacts l, 15 and 16. These contacts are connectedreecti ely through suitable resstances 1, 18 and 19 back to junction 59.Normally grid 52 of tube 53r-is biased above. cutofi by connectionthrough movable contact 13. The normal bias of grit-1 62' of companiontube 60 is below cutofi with reference to its cathode 6| whose potentialis. raised above ground due to the drop in bias resistance 55. Upon theoccurrence of a negative pulse in terminal 50, grid 52 is driven tocutofi. The sharp rise in voltage at anode 56 iscommunicated throughcondenser 65 to grid 62 and causes tube 69 to become conducting. Thisresults in a drop at anode 66 which drop is communicatedthrough blockingcondenser 61 to grid 52. and thus provides for the almost instantaneouschange in. tubes 53 and 60, respectively. After a predetermined intervalof time determined by the constants of the. RC circuit for grid 52, thetwo tubes. revert to their former condition where tube 60 is cutoff andtube 53 is conducting. I'he position of movable contact 13 willdetermine in some measure the speed of return of the multivibrator toits biased condition, in' addition to the RC time of grid circuit 62.The various switch positions are provided for various pulse repetitionfrequencies incident to av change in range of the system.

From anode 56 of tube 53 a connection 85 is taken which goes through ablocking condenser 66 to control grid 81 of an amplifier 88. Ampliher 88has its cathode 89 grounded, or it may be connected through a suitablebias resistance depending upon the characteristics of the tube. Tube 88has its anode 90 connected through a load resistor 9I to wire H whichfor all practical purposes'may be considered who a source of 3+potential. Grid 81 is also connected through a suitable bias resistance92 to wire 1I. Similarly, from the junction of load resistors 69 and 69in the anode circuit of vacuum tube 60 a lead 95. is provided going to ablocking condenser 96 and thence to grid 91 of a vacuum tube, amplifier9 8. Grid 91 is biased by a resistor 91a connected to wire H. Thecathode 99 of this amplifier is connected by a lead I to junction pointIM and which for the present may be considered to be a source of fixedcathode bias. Vacuum tube 98 has its anode I connected through a loadresis tor B96 to wire II.

Anode I05 is also connected through a lead I01 to control'grid I08 ofone'of' a pair of vacuum tubes I09 and II 0 functioning as a split phasesaw-tooth generator. Vacuum tube I09 has its cathode III connected tojunction point II2. Cathode I I 3 of vacuum tube I I0 is also connectedto junction point H2, and this junction point is connected tto groundthrough a bias resistor I I4.

Vacuum tube IIO has its control grid H5 connected to junction point I I2through aresistance II6, and this grid isalso connected through ablocking condenser II1 to a junction point H8. Junction point H8isconnected through resistances II9 and I to anodes I2I and I22 ofvacuum tubes I09 and H0, respectively. Anode I 2| is connected alsothrough a load resistor I25 to a wire I26 which may function as a sourceof B+ potential. Anode I2I is also connected through a resistance I21 tothe movable contact I28 of a switch having three fixed contacts I29, I36and I3I, respectively. These three contacts are connected throughblocking condensers I32, I33 and I34, respectively, to a lead I35 goingdown to wire I01. The positionof movable contact. I28 is governed by theposition of movable contact 13- in the delay multivibrator circuit,since the sweep generating system I09 and IIO andassociated circuitsmust have aisweepdurationproperly correlated with the range of thesys'-.- tem.

Anode I22 of vacuum'tube H0 is connected through aload resistor I31 towire I26. Under normal conditions, vacuum tube 98 conducts so that thepotential at anode I05 is relatively low.

This potential is impressed upon control grid of.

vacuum tube I09. However, cathode III of this vacuum tube is normallybiased through resistonce I I4 so that vacuum tube I09 is normally atcutofi. Upon the occurrence of a positive rectangular pulseat anode I05,grid I08 of vacuum tube I09 goes positive above cutoii and vacuum tubeI09 begins to conduct. This would normally cause the potential at anodeI2I to, drop heavily because of the drop in resistance I25. However, oneofthe three condensers, in this case condenser I32, which hasbeencharged'to apotential existing between 3+ in I26 and the potential atanode I05 begins to discharge through resistance I21. Thetime-constantofthis isadjusted with relation to'the rest of the circuitso that thepotential at anode I.2I drops to form a negative saw tooth. Thisnegative saw tooth' is impressed upon control grid I I5 of vacuum tubeH0 and results in the creation of a positive saw tooth at anode I22 ofthis vacuum tube. The negative saw tooth is conducted from anode I2I oftube I09 by a wire I40, whilethe positive saw tooth is conducted fromanode I22 by a wire I4I.

Wires I40 and MI lead to vertical deflecting plates I42 and, I43,respectively, of a cathode ray tube I44. Connected across wires I40 andMI are resistances I45 and I46 whose junction I41 has'a-groundedblocking condenser I48 connected thereto. Junction I41 is also connectedto one of the focusing electrodes I50 of the cathode ray tube.The-cathode ray tube has horizontal deflecting plates I5I and I 52connected by-leads I53'and I54, respectively, to junction points I56 andI51, respectively. Junction point I56 is connected through a loadresistor I59 to wire I26, while junction I51 is connected through a loadresistor I59 to wire I26. Junction points I56 and I51 connectrespectively to anodes I60 and I6I ofapair of azimuth amplifiers I62 andI63. Am-

plifiers I62 and I63 have their cathodes I64 and. I65'connected throughacommon bias resistance I66 to ground. Contro1 grids. I68 and I69. ofthese two vacuum. tubes are connected to the end terminals respectivelyof a transformer secondary winding I10 having a grounded center tap I1I. Transformersecondary I19 is fed by a primary winding I 13 acrosswhich is connected a potentiometer I14. Oneterminal of potentiometer I14is connected through a dropping resistor I15 to azimuth supply terminal36. It is thus clear that the amplitude modulated azimuth cosine wave isimpressed in push-pull relation on amplifiers I62 and I63. Thus atjunction points I56and I51 there appears an amplified potential whoseinstantaneous value is a function of the azimuth bearing of the antennabeam. This variation in potential thus appears across the horizontaldeflecting plates I5I and I52.

In orderto energize the cathode ray tube, a high voltage source ofpotential is connected across the voltage dividing network consisting ofresistors I80, I8I and I82 in series. The polarityis indicated as shown,and it is understood thatv thevoltage may be something of the order of5,000 or 6,000 volts. Across resistors I8I and I82 are by-passcondensers I83 and I84, respectively; Atthejunction point ofresistors Iand I 8.I-. is connected-a lead. I85 which goes to the remainingfocusing electrode I86 of the cathode ray tube. The most positive partof the resistance dividing network, namely the top end of resistanceI80, is connected to an auxiliary anode I81 within the cathode ray tube,this usually being in the form of a ring of carbonized material on theinside of the glass container adjacent the screen. As is well known, thepurpose of this auxiliary anode is to dissipate the charge in the screenso that no electron repulsive tendencies will be generated within thetube screen.

At the junction of resistances I8I and I82 in the voltage dividingnetwork a lead I81 goes to cathode I88 of a clamping diode I89. AnodeI90 of this diode is connected through a high resistance I9I' to thecathode and is also connected to a lead I92. The cathode ray tube hasits cathode I93 connected by a wire I94 down to lead I92, and this samelead I92 is connected through a blocking condenser I95 to a terminal I96leading to the receiver of the system.

The cathode ray tube has a control grid I91 connected by a lead I98 tocathode I99 of a clamping diode 200. The diode has its anode 20Iconnected back to the cathode through a high resistance 202, and theanode thereof is connected by a line 203 back to the negative terminalof the high voltage resistance network. Diode cathode I99 is alsoconnected through a blocking condenser 204 and wire 205 to the junctionof resistors 51 and 58. It is clear that a negative signal from receiverterminal I96 will be applied across resistor I9I and cause the cathoderay tube cathode I93 to go negative with respect to its control grid.Thus control grid I91 of the cathode ray tube, which is normally atcutoff, rises above cutofi relative to its cathode and renders the beamin the cathode ray tube visible during the time that the signal is on.At the termination of the signal, the normal bias imposed upon cathodeI93 due to the drop in resistance I82 re-appears. By virtue of thepresence of diode I88, the bias of cathode I93 of the cathode ray tubeis kept from being driven more positive than its proper voltage.

Referring back to amplifier 98, it was stated that its cathode 99 isconnected by a lead I to a junction point IOI. Junction point IOI isconnected to the anode 2I0 of a vacuum tube 2I I. Vacuum tube 2II hasits cathode 2I2 connected through a bias resistance 2I3 to ground, andacross this bias resistance a by-pass condenser -2I4-is disposed.Junction point IOI is also connected to an anode 2I6 of a vacuum tube2I1 whose cathode 2I8 has a by-pass condenser 2I9 connected to ground.Feeding cathode 2I8 is a secondary winding 220 having one terminalgrounded so that in efiect it is disposed across by-pass condenser 2I9.Secondary 220 is energized by a primary 22I, and this primary has in itscircuit a blocking condenser 222 and a potentiometer 223 connected toterminal 32 of the elevation potentiometer. Thus cathode 2I8 of vacuumtube 2I1 has impressed thereon a sinusoidal bias whose instantaneousvalue corresponds to the elevation of the antenna beam.

Vacuum tube 2 has its control grid 225 connected through a resistance226 to a wire 221. Vacuum tube 2I1 has its control grid 228 alsoconnected through a grid resistor 229 to wire 221. The two vacuum tubes2 and 2I1 constitute an electronic switch. Wire 221 goes to junctionpoints 230 and 23I and thence to a suitable source of 3+ potential. Fromjunction 230 a series of three resistors 232, 233 and 234,

respectively, go down to anode 235 of a vacuum tube 236. From junctionpoint 23I two resistances 231 and 238 go down to anode 239 of a vacuumtube 240. The cathodes 24I and 242 of these two tubes are connected toground through a suitable bias resistance 243. The anode of tube 236 isconnected through a resistance 245 shunted by a condenser 246 to thecontrol grid 241 of vacuum tube 240. This control grid 241 is alsoconnected to ground through a suitable resistance 248. Control grid 241is also connected to a blocking condenser 250 and lead 25I to anode ofamplifier 88.

Anode 239 of vacuum tube 240 is connected through a resistance 254shunted by condenser 255 to control grid 256 of vacuum tube 236. Thiscontrol grid 256 is connected through a suitable resistance 251 toground. Control grid 256 is also connected through a blocking condenser258 to line 25I going back to anode 90 of amplifier 88.

Control grid 225 of vacuum tube 2II is connected through a blockingcondenser 260 and wire 26I to the junction of resistors 231 and 238. Inthe similar fashion, control grid 228 of vacuum tube 2I1 is connectedthrough a blocking condenser 263 and a lead 264 to the junction ofresistors 233 and 234.

The junction of resistors 232 and 233 is connected by a wire 266,blocking condenser 261 and an additional wire 268 to the control grid210 of a cathode follower tube 21I. Cathode follower 21I has its cathode213 connected through a load resistor 214 to ground, while its controlgrid 210 is connected through a grid resistor 215 to ground. The anode216 of cathode follower 21I is connected to a suitable source of B+potential. Cathode 213 of the cathode follower is connected through ablocking condenser 211 and wire 218 back to right-hand horizontaldeflecting plate I5I to the cathode ray tube.

The operation of the indicating part of the system is as follows. Anegative trigger pulse at terminal 50 generates a substantiallyrectangular wave at the anodes of multivibrator tubes 53 and 60. Apositive pulse at the junctions of resistances 5I and 58 is impressedthrough blocking condenser 204 on resistance 202 and diode 200 whichwill not afiect the pulse. The resistance across the diode issufliciently high so that for the duration of the pulse the control gridof the cathode ray tube is made positive with respect to the cathode ofthis tube. During the existence of this positive pulse on the grid, asignal from the receiver may be impressed upon terminal I96 and tends todrop the cathode of the cathode ray tube with respect to the grid. Thusthe beam will be made visible during existence of the signal coming infrom the receiver. At the same time the negative pulse from terminal I96is applied across resistance I9I so that the cathode of the cathode raytube has its potential stabilized.

Referring back to the multivibrator, the output thereof goes through thetwo amplifiers 88 and 98. The output from amplifier 88 goes to a triggercircuit consisting of two tubes 236 and 240. By virtue of theconnections of these two tubes, a negative gate impulse from amplifier88 will trigger ofi one of the two tubes so that where one tube may havebeen conducting before, it becomes non-conducting, the other tube beingin the reverse condition. Thus, for example, if vacuum tube 236 isconducting, the potential at its anode 235 is at a low enough value-sothat'control grid 24'! of its companion tube 240 is below cutoff. Thenegative pulsefromamplifier 88 is impressed on both control grids ofthese two tubes butwill only affect tube 236. whereupon the anodepotential goes up and results in tube 240 being cut-in.

By having condensers 250 and 258 large in comparison to the remainingcondensers, the time constant of the grid input circuits may be lon andprevent the positive trailing edge of the pulse from triggering thecircuit again.

The conducting condition of tube 236 will cause tube 2|? of theelectronic switch to be cutoff and similarly the conducting condition oftube 249 WilLcause tube 2 of the electronic switch to be cutoff. It isevident, therefore, that as the trigger circuit consisting of tube 236and 240 is switched back and forth, tubes 2 and 2H of the electronicswitch are alternately switched back and forth. When vacuum tube 2 isconducting, vacuum tube 2|! is non-conducting, and the potential in lineI80 is determined by the drop through tube 2. This potential serves tobias cathode 99 of amplifier 98 at a constant level. The output ofamplifier 98 feeds tubes I09 and H with the associated networks ofresistances and condensers to form a split saw-tooth wave appliedrespectively to the two vertical deflecting plates of the cathode raytube.

When electronic switch tube 2|! is conducting, the drop through thattube will be determined by the elevation potential which provides a biasfor cathode 218. Hence this drop through tube 2|! itself furnishes abias for cathode 99 of tube 98 and results in a different bias than whentube 2| I is conducting. This different bias, as pointed out before, isa function of the elevation potential existing at that instant anddetermines the amplitude of the rectangular wave at anode I of amplifier98. This amplitude in turn determines the condition of the sweepgenerating circuit and controls the slope of the voltage curvegenerating the sweep. Thus the vertical sweep base line is changed inaccordance with the elevation of the antenna at that instant.

The horizontal sweep is controlled by the azimuth potentials existing atthe anodes of tubes I62 and IE3. The normal azimuth potential impressedupon the horizontal deflecting plates occurs when the entire indicatingsystem is giving its normal scan. In this condition, vacuum tubeamplifier 98 is biased by means of vacuum tube 2 I l of the electronicswitch. At that instant, vacuum tube 236 of the trigger circuit isconducting, However, when vacuum tube 236 is nonconducting at thenext'trigger pulse from the transmitter, the potential at the junctionof resistance 232 and 233 jumps, and this jump is transmitted throughblocking condenser 26'! and line 268 to control grid 210 of cathodefollower 2'. When cathode follower 2' becomes conducting, the potentialof its cathode 213 jumps, and this positive pulse is transmitted throughblocking condenser 21'! and is superimposed upon right-hand deflectingplate I5l of the cathode ray tube. This tends to pull the electron beamover a predetermined amount above what would normally be due to theinfluence of azimuth potential amplifiers I62 and IE3. When cathodefollower 2' is not conducting, its influence is absent.

In between successive transmitter pulses from the transmitter, vacuumtube 53 of the delay multivibrator is normally conducting. Hence theThistube will be cutoff rpotentialiat the fu ctions of resistanc s 51and 55 is low. .Duri g thattime ,diode 20,0 conducts and permits thepotential of the control gridof the having a directional antenna movablein both azimuth and elevation and having a transmitter and receiver,said transmitter being adapted .to pulse the antenna periodicallyandsaid receiver .being adapted, to receive target echoes during thetime between successive pulses, :a cathoderay tube havinga fluorescentscreen with a base line, means for impressing target echoes fromsaidreceiver as indications on said tube screen, $aid targetindicationsincluding a first indication for each target, located on saidscreen at a point having coordinates defining the range and one of thetwo angular coordinates of said targetmeans for displacing each of saidfirstindications'on said screen to provide a second discrete indicationspaced from said first indication for each target, a second indicationbeing so disposed relative to a corresponding first indication that theline j oining the two forms an angle with respect to said base line todefine the remaining angular co- 1 ordinate of said selectedtarget.

2;The system of claim 1 wherein the original and displaced targetindications consist of bri ht spots.

3. In a radio direction and ra ging system having a directionalantennajmovable in both azimuth and elevation and having a transmitterand receiver, said transmitter 'being' tdapted to pulse the antennaperiodically, and said receiver being .adapted to receive target echoesduring the time between successive pulses, a cathode ray tube having afluorescent screen, means for intensity modulating the cathode ray ofsaid tube with said echo pulses, means for generating a range sweep foreachantenna pulse on said screen along. a first rectangular coordinateaxis, means for displacing said range sweep on said screen along asecond rectangular coordinate axis to define one of two.angularcoordinates of a target, means for defining a first position ofsaidaxis on said tube screen for alternate transmitter pulses to providea first field, means responsive to the remaining angular coordinate ofsaid target for translationally displacing the position of said axesfrom said firstposition to a second position on said tube screen forremaining transmitter pulses to provide a second field, saidsecondfielcl being displaced from said first field so that aline joiningcorresponding points on said two fields forms an angle with one of theaxes substantially equal to the remaining angular coordinateof a target.i

LELAND J. HAWORTH.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS u sn es ept. 28, 19%?

